Highly performant, light and configurable lazy loader in pure JS with no dependencies for images, iframes and more, using IntersectionObserver API
- is a light-weight library, just minified & gzipped,
- has NO DEPENDENCIES :)
- allows lazy loading of dynamically added elements as well,
- supports <img>, <picture>, iframes, videos, audios, responsive images, background images and multiple background images etc.
- even supports LQIP (Low Quality Image Placeholder)
- is completely free and open source.
It is written with an aim to lazy load images, iframes, ads, videos or any other element using the recently added Intersection Observer API with tremendous performance benefits.
Brands using Lozad.js:
and many more...
Table of Contents
- Example with picture tag
- Browser Support
Existing lazy loading libraries hook up to the scroll event or use a periodic timer and call
getBoundingClientRect() on elements that need to be lazy loaded. This approach, however, is painfully slow as each call to
getBoundingClientRect() forces the browser to re-layout the entire page and will introduce considerable jank to your website.
Making this more efficient and performant is what IntersectionObserver is designed for, and it’s landed in Chrome 51. IntersectionObservers let you know when an observed element enters or exits the browser’s viewport.
# You can install lozad with npm$ npm install --save lozad# Alternatively you can use Yarn$ yarn add lozad# Another option is to use Bower$ bower install lozad
Then with a module bundler like rollup or webpack, use as you would anything else:
// using ES6 modules// using CommonJS modulesvar lozad =
Or load via CDN and include in the
head tag of your page.
When loading from CDN, you can find the library on
In HTML, add an identifier to the element (default selector identified is
All you need to do now is just instantiate Lozad as follows:
const observer = ; // lazy loads elements with default selector as '.lozad'observer;
or with a DOM
const el = document;const observer = ; // passing a `NodeList` (e.g. `document.querySelectorAll()`) is also validobserver;
or with custom options:
const observer =;observer;
or if you want to give custom function definition to load element:
If you would like to extend the
loaded state of elements, you can add the loaded option:
"data-loaded"="true"attribute is used by lozad to determine if an element has been previously loaded.
If you want to lazy load dynamically added elements:
const observer = ;observer;// ... code to dynamically add elementsobserver; // observes newly added elements as well
for use with responsive images
<!-- responsive image example -->
for use with background images
<!-- background image example -->
for use with multiple background images
<!-- multiple background image example -->
for use with responsive background images (image-set)
<!-- responsive background image-set example -->
To change the delimiter that splits background images:
<!-- custom delimiter for background images example -->
If you want to load the images before they appear:
const observer = ;observer;const coolImage = document// ... trigger the load of a image before it appears on the viewportobserver;
Large image improvment
Sometimes image loading takes a long time. For this case, you can add a placeholder background:
Lozad sets a placeholder background color of img element and users will see the fallback till the image loads.
Example with picture tag
Create a broken picture element structure.
IE browser don't support picture tag! You need to set
data-iesrcattribute (only for your picture tags) with source for IE browser
data-altattribute can be added to picture tag for use in
altattribute of lazy-loaded images
<!-- For an element to be caught, add a block type that is different from the inline and some min-height for correct caught into view --><!-- NO img element --><!-- instead of img element, there will be the last source with the minimum dimensions --><!-- for disabled JS you can set <noscript><img src="images/thumbs/04.jpg" alt=""></noscript> -->
When lozad loads this picture element, it will fix it.
If you want to use image placeholder (like low quality image placeholder), you can set a temporary
img tag inside your
picture tag. It will be removed when lozad loads the picture element.
<!-- you can define a low quality image placeholder that will be removed when the picture is loaded -->
Example with video
Example with iframe
That's all, just add the
Example toggling class
<!-- content -->
active class will be toggled on the element when it enters the browser’s viewport.
For IE11 support, please make use of these polyfills.
Checkout the FAQ Wiki for some common gotchas to be aware of while using lozad.js
Interested in contributing features and fixes?
See the Changelog